TypeScript Strict Mode

Write and review TypeScript as if strict mode plus the hardening flags (noUncheckedIndexedAccess, exactOptionalPropertyTypes) are enforced, and migrate loose codebases to full strictness flag by flag without breaking the build. Use when someone asks "how do I get rid of any", "turn on strict mode in an existing project", "is this type assertion safe", "why does tsc say possibly undefined", or when writing new…